1. Related Applications
U.S. patent application of L. Young entitled "Differentially Pumped Seal Apparatus" Ser. No. 062,038 06/15/87.
U.S. patent application of L. Young and G. Howard entitled "A Guard Ring For A Differentially Pumped Seal Apparatus" Ser. No. 103,883 filed 10/15/87.
2. Field of Invention
This invention relates to an improvement in particle beam lithography systems for processing a workpiece, such as a semiconductor wafer or mask, and particularly, to an improvement in such systems by providing such systems with a means for preselecting a gap size between the tip of a vacuum seal apparatus and the surface of the workpiece and maintaining this gap fixed during workpiece processing.
3. Prior Art
U.S. Pat. No. 4,524,261 to Petric et al entitled "Localized Vacuum Processing Apparatus" (hereinafter referred to as the '261 patent) and U.S. Pat. No. 4,528,451 to Petric et al entitled "Gap Control System For Localized Vacuum Processing" (hereinafter referred to as the '451 patent).
The '261 patent discloses a localized vacuum seal apparatus, hereinafter called simply a seal apparatus, which provides a non-contacting graded vacuum seal between the seal apparatus and a workpiece to achieve a relatively high vacuum zone in close proximity to the beam of a particle beam lithography system while the remainder of the workpiece remained at ambient pressure as the workpiece is moved in an X-Y direction for processing the entire workpiece. The space between the tip of the seal apparatus and the surface of the workpiece is referred to as a gap.
The U.S. patent application of L. Young Ser. No. 062,038 discloses and claims an improvement over the seal apparatus of the '261 patent in that the Young seal apparatus obtains higher vacuum and a smaller gap between the seal apparatus and the workpiece.
The U.S. patent application of L. Young and G. Howard Ser. No. 103,883 discloses and claims a guard ring of pressurized gas surrounding the seal apparatus to reduce the possibility of contamination coming in contact with the workpiece surface and entering the beam column.
In the '451 patent, it was felt necessary to dynamically control the size of the gap during workpiece processing and thus apparatus for sensing and controlling the gap is disclosed. Specifically, a capacitor sensing device is used to sense the size of the gap and feed this information back to a control and drive mechanism to vary the vertical direction (Z axis) of the workpiece relative to the seal apparatus. The sensing and control is a continuous operation and the gap size is varied within a selected range during workpiece processing.
This invention improves this prior art as disclosed in the '451 patent by providing a means by which a workpiece is held at a predetermined gap size during the processing of the workpiece. This overcomes problems involved in dynamically controlling a variable gap and eliminates the gap size sensors and feedback and drive mechanisms.